Ecological Role of Termites in Dry Environments

Brett Mommer

April, 2003

 

Abstract

 

Termites are predominantly thought of as destructive and menacing creatures that serve only a small part in Earth’s ecology. The contrary, however, is a more accurate description of the incredible niche that this animal fulfills, particularly amid arid and infertile environments. The inhospitable outback of Australia receives a minute amount of annual precipitation. The shortage of moisture has led to an astounding adaption of the few animals that continue living there, notably the termites. Water is required by all living things to stay alive; this fact is not lost on termites. Several species of termites have evolved to such a degree that entire colonies are able to exist entirely within their self-manufactured environments, sometimes even entirely within a piece of dead wood. Recycling everything they use, the termites construct ingenious mounds with their waste materials and prevent moisture from escaping by packing everything together, forming water proof pavements. The termites’ ability to metabolize cellulose with a mutualistic symbiotic relationship allows them to decompose dead plant material and recycle the nutrients back to the environment. Overall, termites are the most important decomposers in dry environments because of their ability to recycle nutrients, form soil, and retain moisture.

 

Introduction

 

It seems natural to dislike termites. Most of them are very small, off-white, alien-looking insects, they live in the darkness, and they have a reputation for being “pests” by causing millions of dollars in damage to wooden structures and vegetation all around the world. Thomas Snyder exhibits this widespread negative view of termites in the title of his 1948 book, Our Enemy The Termite. Nevertheless, recent studies and discoveries have begun to correct the downbeat view of the termite. Surely a creature that exists (or has existed) on every continent in a wide range of environments has a greater ecological niche than a “pest”. Recent studies into the evolution of this order of insects suggests a much more accurate relationship of their contribution to the environment now and in the millions of years they have existed. The termites’ ability to adapt to arid environments has led them to fill the important role of decomposition where common decomposers such as bacteria and fungi cannot function. Australia is an ideal place to study the effects of dry environments on termites because of the low precipitation and elevated heat levels of the desert and savanna.

 

Background

 

Taxonomically, all termites can be placed into Kingdom Animalia, Phylum Arthropoda, Class Insecta, and Order Isoptera. Although termites come in many shapes and sizes, every termite species is common to the Order Isoptera and the current worldwide species count is 2,761. Of the 2,761 species, 1,958 are higher termites. (See Table 1)(Myles, 2003). Lower termites can be described as a set of 6 families sharing the presence of symbiotic intestinal flagellates. Higher termites are further evolved than lower termites in that they have lost the flagellate protozoa and replaced them with bacteria. Higher termites comprise three quarters of all described termite species; many species are yet un-described. (See Table 2)(Myles, 2003). Nevertheless, lower termites are richer in Australia than in other continents while the ratio of the number of species of soil feeding and higher termites is smaller on the island continent.

 

Table 1. Taxonomic distribution of Order Isoptera with Subfamilies of Termitidae (data from Myles, 2003).

[Families/Subfamilies in bold are known to exist in Australia (Krishna and Weesner, 1970).]

 

Family/Subfamily

# Genera

# Species 

Termopsidae 

20 

Hodotermitidae 

19 

Mastotermitidae 

1

1

Kalotermitidae 

22 

419 

Rhinotermitidae 

14 

343 

Serritermitidae 

1

1

Termitidae 

 

 

   Macrotermitinae 

14 

349 

   Amitermitinae 

17 

295 

   Apicotermitinae 

43 

202 

   Cubitermes group

28 

161 

   Termitinae 

43 

288 

   Nasutitermitinae 

91 

663 

Totals 

282 

2,761 

 

Table 2. Isopteran Phylogenetic tree and further differentiation into Families (data from Myles, 2003).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Evolution of Isoptera

 

Termites (Isoptera) are evolutionarily closely related to cockroaches (Blattaria). Termites, mantids, and cockroaches evolved from a common winged ancestor; the three clades are grouped into suborders of the Dictytopera. However, termites and cockroaches are known to have a closer taxonomic relationship than either has to mantids. The correlation of this relationship is seen between two genera: the wood-feeding cockroach (Cryptocercus) and the tropical Australian termite (Mastotermes). The wood-feeding cockroaches share some characteristics of termites (i.e. symbiotic protists in hindgut) and the Mastotermes similarly share some physiological traits and genetic connection with cockroaches (Abe et. al., 2000).

 

The date of evolutionary separation into Isoptera and Blattaria is somewhat ambiguous due to incomplete fossil records, though many relatively recent discoveries have more clearly defined a time frame for such events. The oldest described fossil termite is Meiatermes bertrani, found in limestone in Spain dating to about 130 million years ago (Abe et. al., 2000). Many related fossils have been found in Brazil, Canada, England, France, the United States, China, and in many other countries around the world. Distributions of primitive and modern termites coupled with knowledge of geological events have disproved earlier theories that suggest all termite groups evolved prior to the fragmentation of Gondwana about 180 million years ago. New developments in DNA analyzing technology have led to a new theory. Evidence suggests that many groups of primitive termites were extant throughout the post-Gondwana world (Tayasu et. al., 1998). After the mass extinction of the Cretaceous era however, few of these species persisted. An explosive dispersal wave brought on by the unfilled niche pushed for modern species to emerge and spread utilizing dispersion methods such as land bridges, blowing storms, and floating logs (Abe et. al., 2000). Today, similarities in lower termite species across continents such as Australia, South America, and Africa retain a genetic link from the time they were all joined as Gondwana (Abensperg and Dion, 1997).

 

General Characteristics of Hierarchal Castes

 

Although higher and lower termites differ slightly across species with details of caste differentiation, a generic outline of the termite hierarchy can be easily understood. There are five basic classes within the termite colony (with a few species exceptions): reproductives, winged alates, workers, soldiers, and nymphs (Watson et. al., 1985).

 

Reproductive – One king and queen begin each colony and reside there until killed. The king works to produce sperm to fertilize the queen (she produces up to 3,000 eggs/day). The queen releases hormones that signal differentiation among workers, soldiers, etc. With many species, the life of the mound depends on the life of the reproductives; both the mound and the queen can often be more than twenty-five years of age. In some species, reproductives are replaced when they die allowing the colony to live on, sometimes exceeding a century (Creffield, 1991).

Winged Alates – This most often sighted (and eaten) class of termite functions chiefly in the founding of new colonies. They possess well-developed compound eyes, are capable of flight and reproduction, and can replace the king and queen if they are killed (Watson et. al., 1985). Winged alates are the most common class of termite used for classification due to variations in shape and size of wings. The name Isoptera means “equal-winged” and is given to termites because the two pairs of wings of the winged alates are the same size and similar in appearance (Skaife, 1955). Alates emerge at night to disperse and mate, but they never return to the nest.

Workers – This grouping of termites maintains perhaps the most important role in the colony. Blind, deaf, and sterile, the workers are the smallest active termites (sometimes only a mm or two in length). As the most abundant form of termite, they function in nest building, regurgitating food for soldiers and parents, exploring food and water sources, caring for eggs and younger siblings, and chemically guarding against fungi and other micro-organisms. One of the most important responsibilities of a colony is the gathering of food and water. This important task is carried out by the worker caste (Watson et. al., 1985).

Soldiers – Soldiers are sterile like workers, yet they are not blind. They function in protection of the nest, often becoming suicidal for the good of the colony. The members of this caste have large mandibles (size and shape differs with species) used to slash and lacerate enemies. Soldiers have large heads so they can block entrances from intruders. They also possess frontal projections used to eject defensive chemicals that entangle enemies. When there is a breach in a mound’s wall or a hole in a mud tube many soldiers will rush outside to defend the aperture while workers repair the damage. Frequently the guards are sealed outside the nest and later die of starvation or desiccation (Watson et. al., 1985).

Nymphs – Recently spawned from eggs, nymphs are inactive and undeveloped termites awaiting chemical signals from the queen that lead to differentiation. A relatively small number of nymphs become winged alates or reproductives; a moderate amount become soldiers (10-15% of population) while the majority of nymphs develop into workers (Watson et. al., 1985).

 

Unique Features and Distinct Characteristics of the Termites

 

There is no such thing as an animal that can metabolize cellulose; they do not exist. However, many animals, such as cattle, sheep, goats, deer, koalas and giraffes, consume a great deal of cellulose in their diets. To digest cellulose an organism must utilize cellulase, an enzyme with the ability to catalyze the hydrolysis of cellulose (Ratcliffe et. al., 1952). But these animals do not produce this enzyme; how then do they digest cellulose? This question is answered by a small number of some fairly simple organisms: fungi, bacteria, and protozoans. These organisms (usually bacteria or protozoans) form a symbiotic relationship with their animal host; the symbionts live within the gut of the animal and take part in a (usually) mutualistic relationship. Perhaps the most fascinating feature of termites is their symbiotic relationship with cellulose-digesting organisms. Symbiotic gut protists (lower termites) or bacteria (higher termites) metabolize cellulose from plant material that is ingested by termites (Ratcliffe et. al., 1952). Both termite and microfauna benefit from this relationship: the symbionts obtain a constant supply of food and refuge from the outside environment while the termites acquire glucose and other materials produced from the metabolism of cellulose. Cellulose can be digested easily by the symbiotic gut protists (or bacteria) due to the fact that the cellulosic material has been masticated thoroughly by the host termite. Termites cannot digest cellulose without this symbiotic relationship. The relationship becomes beneficial to both the termite and the symbiont (mutualism)(Ratcliffe et. al., 1952).

           

Termites are soft-bodied and depend on tiny hair-like appendages called sensilla (or setae) to guide them in feeding, defense and reproduction. Little is known of the exact mechanism for their complicated behaviors; it has been hypothesized that termites are born “hard-wired” with the ability to create and react to a complex intermingling of chemical signals and ritualized behavior (Krishna and Weesner, 1969). A rather interesting method of chemical protection of the colony appears when termites produce compounds such as naphthalene for communication and defense against ants, pathogenic microorganisms and nematodes (Krishna and Weesner, 1969). The topic of chemical defensive techniques of termites is a relatively new area currently being studied in the scientific community.

 

Secret Society

 

Termites are highly social and live in colonies of up to one or two million individuals. The “individuals” are mindless and work for the good of the colony; they act collectively as a “super organism” (Skaife, 1955). Little is known of their remarkable organizing ability except that they communicate with a series of pheromones. (See section on communication) Although a colonial social structure exists resembling ants or bees, the termite evolved before and apart from other types of colonial insects (Watson et. al., 1985).

 

The termite society as a fundamental unit in evolution (which is composed of many multicellular individuals) has analogies to an individual organism. The ideal analogy for this resemblance, borrowed from the 1969 publication Biology of Termites (Krishna and Weesner, 1969), illustrates perfectly the interconnection within a termite colony:

 

“The superorganism has division of labor, integration, and specialization between individual castes, with the sterile castes analogous to the somatic cells of an individual organism, the reproductive castes paralleling its gametes, and the functions of the workers and soldiers analogous to the functions of its nutritive and protective cells. The individuals in a termite society cannot exist by themselves, and their interdependence and integration resemble those of an organism. Like organisms, termite nests are homeostatically regulated units. The nest wall serves as a barrier to predators in a manner similar to that of the shell of an animal. The internal environment is self-regulating, optimal for existence and survival, and to some degree independent of the external environment. Nest parts may be regenerated, like the lost parts of an organism. Similarities are also found in growth, development, symmetry, and adaptation.” (Krishna and Weesner, 1969).

 

Communication

 

Termites cannot communicate visually or with sound for the simple reason that they have no sight and they are deaf. (See also blindness section) Instead, this order of insects communicates utilizing the taste and touch senses. Termites have the ability to recognize nest mates by their special odor; the same way male reproductives locate females by means of scent (Limburg, 1974). Termites request food by touching each other in a particular manner. They leave scent trails to food sources outside the nest. When a foraging termite finds a new supply of food, it runs back to the nest with a particle of food in its jaws, leaving a trail of scent behind it. It pushes the other termites around to attract their attention; it also shoves the morsel of food at them. This entices them to follow the trail to the fresh source of food. The scent that they follow comes from a gland on the underside of the termite’s abdomen. Scientists believe that the scent trails originally evolved as an alarm signal to direct worker termites to a rupture in the nest, through which enemies could enter to consume the soft, succulent inhabitants (Abe et. al., 2000). Blind as they are, the termites can somehow sense the light that comes in through the opening. They are also exceptionally sensitive to the faint currents of air that waft in or out. The termites near the scene of the break scamper back to the center of the nest, laying a scent trail and alerting the other termites with their anxious movements. The scent is a substance known as pheromone, which induces certain reactions from termites and other insects. In this case, it permits them run back along the scent-marked path to the opening, which they instinctively seal up again (Limburg, 1974).

 

Blindness

 

Since almost all termites live in total darkness their entire lives they have lost the ability to see and are blind. Being continuously secluded from normal light and radiation, termites have little necessity for pigmentation as a filter against ultra-violet light. For this reason, their integument is either translucent or poorly pigmented (Creffield, 1991).

 

Types of Nests

 

Termite nests can be found in a variety of shapes and sizes depending on the age of the mounds and the species that construct them. Four general types of nests appear around the world: arboreal, subterranean, mound, and one-piece nests. Arboreal nests are often extensions from nests below ground connected by shelter tubes to a crotch or branch in a living tree. Termites never wander unprotected in the open air but instead build tubes composed of carton. Carton consists of earth and fecal material cemented together with saliva (Abe et. al., 2000). This combination becomes very durable when allowed to dry and creates perfect shelter tubes, sometimes covering the entire surface of a tree. These shelter tubes are used to connect subterranean nests with arboreal nests and also cover impenetrable surfaces to provide a dark and damp passage (Snyder, 1948).

 

Termites, unlike houseflies, have no sticky pads on their feet, therefore they cannot crawl up a windowpane and they encounter difficulty walking over smooth surfaces. To battle this problem they coat everything with their excrement; this creates a non-skid surface for ease of walking (Skaife, 1955).

 

Below ground nests are common where moisture remains at low levels throughout the year for the reason that construction of a subterranean nest minimizes evaporation and desiccation. In the case of subterranean termites, gigantic systems of underground tunnels and galleries can reach hundreds of feet to food sources, covering acres of land (Snyder, 1948). A royal chamber (queen cell) is always present in the center towards the base of the nest where the reproductives are kept moist and well fed. When a colony becomes too oversized for the queen to keep up, secondary reproductives are created and satellite colonies emerge nearby to supplement the primary colony (Pearce, 1997).

 

Although below ground nests are more or less protected from large predators, there is a threat of invasion from tunneling animals, carnivorous nematodes, and anything else that could enter the nest from underground. To protect a subterranean nest from such attacks, an astounding feat of natural engineering arises as a result of millions of years of defensive evolution. Using a combination of earth, clay, sand, fecal material, and saliva the colony fabricates a thick, rock hard, waterproof pavement surrounding the nest. This impermeable barrier serves as a device to produce a self-sustaining environment as well as for protection of the settlement (Snyder, 1948). The watertight fortification also prevents water loss and reduces diffusion of the queen’s scent; the scent is amplified by confining it to the small area of the nest thus increasing its effectiveness. A predicament develops, however, due to subterranean nests’ airtight construction (Pearce, 1997). Rising carbon dioxide levels are poisonous to termites and several gases are produced that must be expelled from the nest. To clear this obstacle, another inventive process takes place within the nest. Instead of ventilating the nest with hot dry air from the exterior that would dehydrate the colony, a system is set up to ventilate with cold moist air from below. (See section on desiccation) With differential air pressure and specialized air chambers, the nest is kept well ventilated and water loss is all but eliminated (Snyder, 1948).

 

Termite mounds (also known as hills) are probably the most interesting and straightforward indication of termite presence. Many species build mounds, albeit for different reasons. Humans have contemplated termite mounds for thousands of years attempting to fathom how insects so small, blind, and mindless have such extraordinary and ingenious construction abilities. A variety of mound shapes and sizes can be constructed from almost any material found or excreted by termites. Mounds are above ground and, depending on the species, can serve a plethora of uses including: a storage room, temperature control device, emergency residence, refuge from flooding, apparatus for ventilation, or as the entire nest itself (Snyder, 1948).

Termite mounds in the savannas: there can be as many as 100 per hectare                                   Magnetic termite mound

 

(Left) Termite mounds cluster a savanna in Australia; mounds can reach several meters in height. (Right) Magnetic mounds are a remarkable phenomenon of evolution. Always oriented north, they regulate mound temperature throughout the day, exploiting heat from the sun at dusk and dawn while protected from overheating at noon.

Photos courtesy of http://savanna.ntu.edu.au/information/ar/ar_te.html

(Martin, 2000)(Illustration: © Geoff Thompson)

 

As with any structure in biology, form reflects function. A mound with a large durable rounded peak, as is found in many tropical regions, functions to repel water from the mound during heavy rainstorms. A tall slender mound, similar to those often found in hot and temperate regions, acts to regulate temperature throughout the day (Skaife, 1955). Termites in different areas have evolved to build mounds depending on local environmental conditions: daily and seasonal variations in temperature, precipitation, light intensity, etc. Magnetic mounds are at first puzzling; they take a thin wedge shape and are always oriented in a north-south direction. Through a remarkable phenomenon of evolution, the species that construct magnetic mounds have capitalized on their position in reference to the Sun and Earth. The mounds always point to the Earth’s north magnetic pole, though magnetism has nothing to do with these termites. The reason for pointing their mounds in a north-south direction is directly related to the daily change in temperature associated with the local environment (Martin, 2000). The days can be sweltering while the nights can be frigid; how does the mound deal with the temperature extremes and stay at a relatively constant temperature? It is the orientation of the mounds that allow them to take advantage of the sun’s light energy. When the sun rises in the morning, the broad eastern side of the mound absorbs heat to recover from the cold night. In the middle of the day, only the top ridge of the mound is in line with the sun’s rays; this prevents the mound from overheating in midday. During sundown, the western side of the mound is heated to counter the upcoming cold temperatures of night (Martin, 2000).

 

The final category, one-piece nests, is truly quite interesting. Colonies of this type are confined entirely within dead wood and are able to survive years without regular replenishment of water. Functions within these termite nests are difficult to study due to their sealed environments. What is known is that the colony creates a hollow chamber and seals it from within with mud to form a waterproof barrier that holds moisture in. This method of living is very beneficial during periods of extremely dry weather. It also played an important role in dispersal of species using logs to transport across oceans and down rivers (Limburg, 1974).

           

Habitat

 

Termites retain the ability to thrive in every type of terrestrial environment where enough food is present (although mostly in warm regions). Nests can be found in areas of varying annual precipitation, from tropical rainforests to arid deserts. Individual colonies maintain the ability to remain self-sustaining for very long periods without regular precipitation or water replenishment. Living termites (or termite fossils) are present on every continent including Antarctica (Davies and Williams, 1978).

 

Foraging, Feeding, and Digestion

 

Termites can be divided into four groups with respect to feeding patterns: wood-feeders, soil-feeders, leaf-litter harvesters, and fungus growing/feeding. Wood-feeding termites can be divided into more accurate groups, (rottenwood, dampwood, drywood, etc.) but their descriptions are somewhat ambiguous. The term “wood-feeders”, for all practical reasons, will suffice. Subterranean termites reach sources of food by constructing underground tunnels (foraging galleries), which branch out from the nest. Usually only the workers and soldiers visit feeding sites but every so often nymphs will be there. The reproductives, alates, and eggs almost always stay in the nest. Foraging termites are attracted to moisture and timber, particularly that which is in an early state of decomposition by wood-rotting fungi and which is either laying on or buried in the ground (Creffield, 1991).

 

Depending on the preferences of the species, termites feed almost exclusively on wood, soil, and leaf litter. Cellulose is the desired product that is usually in great abundance wherever termites are found. Although some termites have been found attacking grain, dung, and bone, highly cellulosic materials such as wood and litter are the preferred food. Lignin, although indigestible in most species, is used to reinforce nest material and shelter tubes. Nothing is wasted in the colony; termites eat their dead, recycling nitrogen and protein (Snyder, 1948). Cannibalism, in fact, is one of only two means of acquiring protein. The only other method of obtaining protein is through the eating of fungal hyphae growing on decaying plant material. Due to the termites’ ingestion of almost exclusively cellulosic material, protein is a valuable commodity within the termite colony. When a member of the colony is injured or killed, fellow termites quickly eat the body (Ratcliffe, 1952). This may seem malicious, but it is essential and beneficial to the life of the colony by recycling protein and preserving water, an economically clever practice in arid environments.

 

Workers share the contents of their stomachs (including symbionts) through regurgitation. Soldiers, nymphs, and reproductives cannot consume food for themselves so they rely on workers to regurgitate food for them. This is the mechanism for every termite getting the symbiotic microorganisms in their guts. Trophallaxis is defined as the mutual exchange of food between members of a colony (Snyder, 1948). Termites employ trophallaxis by regurgitating predigested cellulose when nestmates gesture them to do so. Trophallaxis is a continuous process within every termite colony, which ensures that every member is fed. The process is ongoing and continuously repeated with every termite, even nymphs. In fact, nymphs contain intestinal protozoa 24 hours after hatching indicating trophallaxis occurs immediately after hatching (Snyder, 1948).

 

Wood feeding termites hold the ability to hollow out wood from within without penetrating the surface. It is thought that the worker termites that excavate this material maintain the ability to sense temperature differences when approaching the exterior and move to another location. This way, trees are hollowed from within and are weakened, but remain living (Martin, 2000). For this reason termites are very unpopular with the timber industry, although the cavities make a perfect shelter for other animals (didgeridoo makers do not object either). Wooden supports in homes are often hollowed from the interior, leaving nothing but a wooden shell to support the house; this also generates resentment towards termites. Millions of dollars in residential damage is caused by termites every year and is usually not covered by insurance. The blame for this damage lies with only a few species (Creffield, 1991).

 

Predators

 

Termites are an essential part of the food chain and an important source of food for many animals. Winged alates emerge as swarms of millions that provide a feast for birds, lizards, snakes, frogs, ants and other insects (Pearce, 1997).

 


Termite nests are also frequently attacked or probed and used as primary food sources for many species. The reduvid (assassin bug) pierces into the tunnel of a nest and sucks in termites. Small marsupials (dunnarts, numbats, etc.) and reptiles (lizards, geckos, skinks) also attack termite mounds for sustenance. The golden bandicoot and bilby tunnel next to a mound where they wage their attack. Echidnas depend on termites in their diet; they search out a mound, dig into it with specialized claws, and lap up termites with a long tongue (Martin, 2000). It is thought that termites may be largely responsible for the great diversity and abundance of animals in arid parts of Australia. Termites may also be an essential source of water for many animals in dry environments where water is a priceless commodity. This makes nests into

“water banks” and designates termites as a vital foundation of many dry ecosystems (Martin, 2000).

Many animals also use termite mounds as nesting sites, these animals are known as squatters. Parrots and other birds dig nests into termite mounds during the wet season. While making their nests, Australian kingfishers fly head on, crashing into the mound to create an initial hole. Sometimes this process is fatal if the mound is too dry. A plethora of geckos, pythons, beetles, and mice use termite mounds for usual residence or in an emergency situation as a place to hide from enemies. A species of monitor lizard lays its eggs in a mound and, acting instinctively, the termites seal the hole. The monitor’s eggs are then incubated by the mound’s constant temperature until they hatch. At that time the mother must return to dig the newborns out of their enclosed nursery (Martin, 2000).

 

Ecologically Significant Processes

 

Most termite species in Australia are responsible for detritus consumption. Their role as detritivores is one of the most important factors in the long-term balance of the ecosystem. Detritus litter consumed by termites is composed of wood, grasses, humus, and other material. The detritivorous recycling of lignocellulosic materials accomplished by termite colonies leads to soil formation. Termite colonies also act as mediators in arid environments by controlling accessibility of litter to other decomposers (Park et. al., 1996). In many settings, termites are responsible for the removal of up to 100% of herbaceous matter and may also take part in changing soil structure and increasing effects of erosion. The balance between termites and their environment is geomorphological as well as ecological. By promoting seasonal moisture diffusion along their galleries, termites allow the granite bedrock to erode at about the same rate as they are removing weathered material from the soil (Davies and Williams, 1978).

 

For a steady plant community to arise and persist, a delicate natural balance must exist involving plant growth, plant consumption by animals and insects, and soil development through rock weathering and re-cycling of nutrients from broken-down plants (Davies and Williams, 1978). Termites play an important role in nutrient dynamics by ingesting and redistributing minerals, fatty acids, vitamins, and 20 amino acids (Pearce, 1997). Nutrient cycling of phosphorus, carbon, and nitrogen results from the metabolic processes carried out within colonies. Carbon input from annual litter consumption is mineralized to carbon dioxide and methane by the termite gut microfauna. Termites participate in the essential function of nitrogen fixing that in turn affects the environmental nitrogen balance. Their contribution to the soil nutrient budget is evident in their mineralization of carbon, which is responsible for up to 20% of carbon mineralized in the ecosystem (Park et. al., 1996). The degree of nutrient processing within mounds is related to mound moisture and temperature. Water and nutrients are redistributed from pavements to surrounding regions within the soil. Termites’ ability to turn over plant nutrients has led to rich patches in an environment where moisture is limited (Park et. al., 1996). Termite modified soils affect the soil chemical parameters and nutrient availability to nearby vegetation. Plant species composition changes with increasing distance from mounds, especially amid infertile soils. All soils in nests are more acidic than surrounding soil and nutrient levels in nested soils are higher than in un-nested soil (Park et. al., 1996). Nutrient levels are generally higher in woodland than shrubland mounds due to the increased availability and variety of nutritional materials.

Soils surrounding termite nests also have a massive increase in fertility due to the higher nutrient status of materials eroded from mound surfaces. The increased nutrient levels of soil eroded from nests changes vegetation patterns in neighboring areas. Mounds form a significant bank of nutrients that are temporarily withheld from plant growth (Park et. al., 1996). Nutrients are eventually returned to the soil surface by erosion of abandoned mounds; the time for release depends on the degree of erosion and the longevity of mounds. An average mound turns over 300-400 kilograms of soil material a year (Abe et. al., 2000). This process allows nutrients trapped in dead plant material to be released back to the environment. Growing plants then reuse the nutrients and the cycle continues. This system of nutrient cycling has an enhanced role in nutrient-impoverished sites due to termites’ ability to exploit low fertility systems. In fact, the diversity of termites is associated with infertile soils and has profound implications for the size structure of the vertebrate community. There seems to be a complimentary distribution of areas of high diversity of termites and native herbivorous mammals in Australian savannas and deserts. Termites often act as primary decomposers in dry climates where there is not enough moisture for organisms such as fungi, earthworms, micro-bacteria, and beetles (Abe et. al., 2000). In dry environments termites are the main decomposers throughout the year due to their inventive ability to prolong desiccation and avoid dehydration.

 

Desiccation

 

Termites may cease foraging near the surface of the soil during periods of hot dry weather. When there is an extended period without water replenishment, moisture is absorbed by tunneling down and transporting damp earth or sand into the nest. Subterranean termites spend their entire lives in the galleries and tunnels within their nest (except for the winged alates when emerging to mate)(Creffield, 1991). Conditions in the nest are uniform and fairly constant: total darkness prevails at all times, humidity is elevated, and temperature fluctuations are minimized. Termites have become so specialized that these are practically the only conditions they can now endure for any amount of time. Since their activities are restricted to a covered passage system in which the relative humidity is always high, their integument does not need to be a good moisture barrier. In fact, it is very permeable so that when termites are exposed to a dry atmosphere they lose moisture and soon die from desiccation (Creffield, 1991).

 

Excrement

 

The ability to retain water is especially important in hot dry environments where precipitation and moisture levels are extremely low. Many species of termites normally void liquid feces when there is enough water to go around and the risk of desiccation is very small. It is when humidity and moisture levels drop to dangerous levels that many adapted species exhibit perhaps the most interesting method of water retention; instead of amorphous fluid-like feces, a plug of hard dry material is voided from the anus. Rectal glands of varying complexity produce these pellets. At their most elaborate these glands consist of six conical pads of cells projecting into the lumen of the gut separated from each other by elaborately convoluted channels (Krishna and Weesner, 1969). The function of the rectal glands in reabsorption of water in termites is coupled with tall elaborate rectal pads. Heavy bands of circular muscle surround the posterior portion of the rectum and provide powerful contractions to squeeze fecal pellets free of water. Radially arranged bundles of muscle on the body wall and attached to the rectum completely exhaust fecal material of water before it is expelled (Krishna and Weesner, 1969).

 

Possibilities for Future Research and Application

 

A great deal of information is already known about termites and their general functions. Some data, however, is very difficult to collect. Sampling termite populations has traditionally been difficult for biologists; improved methods of population sampling are continually being developed. Soil formation processes, although understood, lack consistent data; this area requires intensive studies. Termites are theorized to have the ability to mineralize manganese and a number of other minerals, warranting the need for a more thorough study of termites’ role in nutrient cycling. It is thought that termites could be utilized for the decomposition of lignocellulosic wastes produced by humans. At some point in the future, landfills, litter, and animal waste could be replaced by soil with the use of termites as waste recyclers (Pearce, 1997). Possible fields of interest for those interested in termites include but are not limited to agronomy/agriculture, biogeography, ecology, forestry, metabolism, microbiology, physiology, soil-science, ingestion studies, isolation effects, and taxonomical research/discovery of new species and their role in the environment.

 

Conclusion

 

Termites have been around for millions of years. Only within the past century or so have they been studied scientifically. Perhaps the most important ecological function of Isoptera in dry environments is the role of nutrient recyclers. Termites are the principal decomposers of cellulose, a material they could not digest without the help of symbiotic gut microbes. Their role in the ecology of Australia’s savannas and deserts is necessary for the long-term balance of nutrients in the soil and for the creation of the soil itself. With almost 3,000 species, Order Isoptera continues to evolve and become more and more specialized for a variety of climates.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

References

 

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Abensperg, T.M. and Dion, S. 1997. Latitudinal gradients in the species richness of Australian termites (Isoptera). Australian Journal of Ecology 22 (4):

471-476.

 

Creffield, J.W. 1991. Wood-destroying insects, wood borers, and termites. Collingwood VIC, Australia: CSIRO Publishing

 

Davies, J.L. and Williams, M.A.J. 1978. Landform Evolution in Australasia. Canberra, Australia: Australian National University Press.

 

Krishna, K. and Weesner, F.M. 1969. Biology of Termites. Volume 1. New York: Academic Press.

 

Krishna, K. and Weesner, F.M. 1970. Biology of Termites. Volume 2. New York: Academic Press.

 

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Martin, S. 2000. Termites. Tropical Topics 64: 1-6. Environmental Protection Agency: Queensland Parks and Wildlife Service.

 

Myles, T.G. 2003. Phylogeny and Taxonomy of the Isoptera. <http://www.utoronto.ca/forest/ termite/speclist.htm> and <http://www.utoronto.ca/forest/termite/phyltree.htm> Accessed 2003.

 

Park, H.C., Orsini, J.P.G., Majer, J.D., and Hobbs, R.J. 1996. A model of litter harvesting by the Western Australian wheatbelt termite, Drepanotermes tamminensis

(Hill), with particular reference to nutrient dynamics. Ecological Research 11 (1):

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Pearce, M.J. 1997. Termites: Biology and Pest Management. New York: CAB International.

 

Ratcliffe, F.N., Gay, F.J., and Greaves, T. 1952. Australian Termites: The Biology, Recognition, and Economic Importance of the Common Species. Melbourne,

Australia: Commonwealth Scientific and Industrial Research Organization.

 

Skaife, S.H. 1955. Dwellers in Darkness. London, New York, Toronto: Longmans Green and Company.

 

Snyder, T.E. 1948. Our Enemy the Termite. Ithaca, New York: Comstock Publishing Company.

 

Tayasu, I., Inoue, T., Miller, L.R., Sugimoto, A., Takeichi, S., and Abe, T. 1998. Confirmation of soil-feeding termites (Isoptera; Termitidae; Termitinae) in

Australia using stable isotope ratios. Functional Ecology vol. 12 (4): 536-542.

 

Watson, J.A.L., Okot-Kotber, B.M., and Noirot, CH. 1985. Caste Differentiation in Social Insects. Oxford, New York, Toronto, Sydney, Paris, Frankfurt: Pergamon Press.